The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In drilling operations such as those used in the construction of oil and gas wells, a tubular casing is generally run into the borehole and cement allowed to set in the annular space outside the casing to support or consolidate the formation before resuming drilling at a smaller diameter. However, it can be useful to be able to consolidate a weak zone without setting a casing thus avoiding a cementing operation and allowing a swifter drilling.
‘Wellbore consolidation’ is the process by which a wellbore is kept firm, secure or compact during drilling or cementing, or during simulation and fracture operations, so that lost circulation of fluids from the well through fractures, which can occur in any formation, is prevented. Consolidation is typically provided by mechanical or chemical means.
Mechanical means of wellbore consolidation include using setting casing or solid expandable tubulars to cover the problematic zone. Usually, a tubular casing is generally run into a borehole, and cement allowed to set in the annular space to consolidate the formation before resuming drilling at a smaller diameter.
Chemical means of wellbore consolidation involve either injecting chemicals into the naturally unconsolidated formation to provide in situ grain-to-grain cementation, or creating a good filter cake on the surface of the problematic zone. These can be performed while drilling (through drilling fluids) or after drilling through physical and/or chemical interaction of a fluid with the formation.
Fibres are already used in the oil and gas industry to prevent lost circulation during drilling (US 2006/0042797; US 2006/0019834; US 2005/0187113) and/or cementing (US 2005/0139130; WO 2005/110942). Such fibres form a net/mat inside fractures, thereby preventing fluids from entering formations. Fibres are also used during stimulation and fracture operations (U.S. Pat. Nos. 7,004,255; 6,192,985; US 2003/0054962; US 2004/0177960; US 2005/0245401; US 2005/0175654; US 2006/0283591).
In the textile industry, techniques have been proposed which involve the production of bonded, non-woven fibrous batts by the use of dry, solid, particulate, latent-cross-linkable, thermosetting, fiber-binders (U.S. Pat. No. 6,039,821; WO 1999/064656). The fibre-binder contacts the fibres to form a raw batt, with the fibre-binder loosely adhering to the fibres of the batt. The raw batt is then heated to effect the melting of the fibre-binder, which flows to intersections of the fibres then reacts with cross-linking agents with terminal reactive groups of resin, so that the raw batt is converted into a hot cross-linked batt which is then cooled to room temperature.
The polymeric component of such fibres can be heated through other means. It has been disclosed in WO 2003/063548; Gillespie et al., and many other references, including: Suwanwatana et al., Composites Sci. and Tech., 66, 1713-1723 (2006); Yarlagadda et al. J. of Thermoplastic Comp. Mat., 11, 231-337 (1998); Kim et al., Adv. Comp. Mat., 11, 71-80 (2004) that small particles of electrically-conductive and magnetically-conductive materials (‘susceptors’) added into thermoplastics, which are neither electrically-conducting nor magnetically-conducting, would allow hysteresis losses; this in turn heats the susceptors and causes the thermoplastics to melt. When designed as a film between two pieces, this method allows welding to take place.
In the aerospace science industry, this method has been used to strengthen structures. Electrically conductive carbon fibres are coated with a heat-crosslinkable polymer and assembled into structures, then heated by resistive heating to allow the crosslinkage and toughening of the structure (Naskar et al., Journal of Composite Materials, 40(20), 1871-1883 (2006); Sarles et al., Proceedings of SPIE—the International Society for optical Engineering, 6173, art. no. 617316 (2006)).
This invention is based on the use of similar techniques in the oil and gas industry, the method resulting from this involving elements of both mechanical and chemical means of wellbore consolidation. In this way, weak zones can be consolidated without the need to set a casing or without the need for cementing. As a result, the drilling process can be speedier in such zones.